The technology involved in producing and pumping lightweight concrete is well known in the prior art. It can generally be achieved using two types of density modifiers, namely foam and lightweight aggregate.
Foamed concrete is made by introducing a water-based, gas-filled foam into a paste that is typically formed with water and Portland cement alone or Portland cement with a fine, lightweight aggregate. The foam structure is developed by adding a gas-generating chemical to the Porland cement paste, or by mixing a pre-formed, water-based foam into the cement paste to achieve a density below 1000 kg/m3.
The latter method requires that Portland cement be mixed with a pre-formed aqueous foam that is produced using a commercial foaming agent, such as a hydrolysed protein. This approach requires a foam generator on site to make the foam.
Correct ratios of foam to concrete, particularly at the job site, are difficult to maintain. This difficulty can lead to the possibility of non-uniformity of the final foamed concrete produced, as well as variable mix quality, pumpability, extrudability, and finishing characteristics. The problems are exacerbated by the fact that the foam begins to collapse from the moment it is formed since the foam is not self-generating.
Lightweight aggregate concrete, made by mixing lightweight aggregate such as expanded polystyrene, perlite and vermiculite together with a mortar is mainly targeted at applications with concrete density above 1000 kg/m3. Difficulties arise, however, in mixing the cementitious slurry and the lightweight aggregate due the tendency of the aggregate to clog and segregate because of its inherent composition and low specific gravity.
To make such polystyrene concrete pumpable, it may be necessary to increase the water content in the mix to overcome friction in the pipes. This tends to aggravate the segregation and clogging problems associated with lightweight aggregate concrete production.
Such lightweight concretes ie. foamed concrete and lightweight aggregate concrete have been used as core infill for sandwich panel walling but are subject to certain difficulties.
Foamed concrete exhibits a high hydrostatic pressure during core filling which sometimes necessitates the use of structural formwork bracing during core-filling of sandwich walls. The mix may also collapse heavily during pumping and pouring from the top of the wall height down into the wall cavity.
As far as lightweight aggregate concrete is concerned, core infill needs to exhibit a density of 1000 kg/m3 or below, which is outside the normal density range for lightweight aggregate concrete. To achieve this, up to 1 m3 of bulk lightweight aggregate volume per 1 m3 of mix is needed to be incorporated in the mix. This leads to difficulties in the coatability of lightweight aggregates due to the insufficient mortar volume present which consequently results in poor mix homogeneity and insufficient bond between the mix constituents.
The inclusion of air-entraining agents (AEAs) to improve freeze/thaw durability, aid pumpability, improve workability, and lower the density of concrete has long been practiced in the art. The AEA dose was normally specified to range between 5% to 9% air volume in the mix, with air content limit set to a maximum of 22% by ASTM C-150. Air contents higher than this were normally avoided, especially in pumped concrete, for a range of reasons including:
during pumping a highly air-entrained concrete, the air bubbles tend to break upon impact with the pipe walls, joints elbows, forms, and the like which leads to variable air contents in the placed concrete;
the pumping stroke can be absorbed by the compressible air enclosed by the pipeline, leading to pumping failure;
the compressibility of excessive air during pumping will reduce its effectiveness as a workable medium and make it more difficult to place;
excessive air in the mix can cause the placed wet concrete to collapse due to the instability of the air-void system; and
highly air entrained concrete can lead to excessive reduction in the strength of the hardened product.
It is an object of the present invention to overcome or ameliorate one or more of the disadvantages of the prior art, or at least to provide a commercially useful alternative.